As a naturally occurring analog of psoralen and an isomer of methoxsalen 5-methoxypsoralen (hereinafter "5-MOP") is found in a variety of plants.
5-MOP has been employed in the treatment of psoriasis (See, e.g., the following: Belgium Patent No. 821,424 (Goupil), Feb. 2, 1979, which discloses pharmaceutical compositions for treating psoriasis containing 100 to 1000 ppm 5-MOP; U.S. Pat. Nos. 4,217,445 and 4,429,138 disclose processes for synthesizing 5-MOP; U.S. Pat. No. 4,699,781 discloses sun tanning products containing between about 2.75 to 27.5 mmg, i.e., mg 5-MOP per 100 gm of the product, an ultraviolet-B filtering agent and an oily excipient). It has also been proposed to use 5-MOP in the treatment of psoriasis when administered in combination with ultraviolet-A radiation (see H. Hoenigsmann, et al., Brit. J. Dermatol. 101: 369, 1979).
5-MOP has also been used to treat superficial skin cancers, such as dyskeratosis due to exposure to the sun, preinvasive epithelioma and basocellular epitheliomas (LaneBrown, M.L. and P. Forlot, "Photo-Onco Therapy (POT): An Alternative Modality for the Treatment of Superficial Skin Cancers", Ann. Dermat. Venerol., 111(9):851, 1984; and J. Invest. Dermat., 87:382, 1985. The acute effects which occur in humans with 5-MOP administration has also been investigated. Among such effects are increases in plasma melatonin levels at different times of the day, and retinal sensitivity to light.